CHAPTER XXIV. 



SPECIAL TESTS WITH REGARD TO IRON. 



1. Youngs Work. 



IN the last chapter I gave the sun-spot observations in their 

 most general form, represented by Fig. 106, in which we had 

 the Fraunhofer lines compared with the lines widened in spots. 



Now if I had contented myself with such maps as that a 

 portion of which was selected to engrave the figure in question, 

 it might, and it certainly would have been said that nothing 

 was more natural, that in fact the only result which had been 

 got out, was that there was more of one chemical element in one 

 spot and more of another in another ; and 'that the inversions 

 were simply due to this cause. I have already shown, how- 

 ever, that we have got far beyond that, and that the inversions 

 are truly inversions of lines of the same metal. This is one 

 of the points to be strengthened in the present chapter. 



These results have been mapped in all their details in another 

 long series of maps of a different kind, the difference being 

 that instead of considering all the Fraunhofer lines and all the 

 lines recorded in spots and prominences, we have a map for 

 each hundred observations, strictly limited, both as regards sun- 

 spot and prominences, to one metal. 



I propose in this chapter to refer specially to this latter series 

 of maps. 



Part of the work which has been undertaken in connection 

 with this special branch of the investigation in order to enable 



